This invention relates to a fluid pressure braking system and stop light control circuit for a towed vehicle.
Heavy duty vehicles, normally consisting of a tractor and at least one trailer, are normally equipped with a fluid pressure braking system. More recently, it has also become common for such vehicle to be equipped with an adaptive braking system which responds to an incipient skidding condition of a vehicle wheel to control wheel lockup. It is also has become increasingly common for a single tractor to pull two or even three trailers in a so-called "turnpike train". The adaptive braking system on such vehicles is powered by the stop lamp circuit. Because each of the tractor, trailers and dollies (which must be used with second and third trailers) are equipped with their own set of stop lights, power consumption due to stop lamp draw can be as high 15 watts per vehicle. This can result in a significant voltage drop to the antilock systems used on these trailers and dollies, which can significantly reduce the voltage to the antilock modulators, and may cause them to malfunction. However, it is not necessary that the stop lamps on the intermediate trailers and dollies be operated, although these vehicles must be equipped with stop lights because they may on occasion be used as the last unit in the vehicle train. By not illuminating the stop lamp on intermediate units preceding the last unit of the vehicle train, power is conserved, and sufficient voltage to assure proper operation of the antiskid system at all times is assured.